The History of Arda is divided into three time periods, known as the Years of the Lamps, Years of the Trees and Years of the Sun. A separate, overlapping chronology divides the history into 'Ages of the Children of Iluvatar'. The first such Age began with the Awakening of the Elves during the Years of the Trees and continued for the first six centuries of the Years of the Sun. All the subsequent Ages took place during the Years of the Sun. Most Middle-earth stories take place in the first three Ages of the Children of Iluvatar.

Music of the Ainur

The supreme deity of Tolkien's universe is called Eru Ilúvatar. In the beginning, Ilúvatar created spirits named the Ainur. Ilúvatar made divine music with them. Melkor, Tolkien's equivalent of Satan, who was then one of the Ainur, broke the harmony of the music, until Ilúvatar began a third theme which the Ainur could not comprehend since they were not the source of it. The essence of their song symbolized the history of the whole universe and the Children of Ilúvatar that were to dwell in it — the Men and the Elves.

Then Ilúvatar created Eä, the universe itself, and the Ainur formed within it Arda, the Earth, "globed within the void": the world together with the airs is set apart from Kuma, the "void" without. The first 15 of the Ainur that descended to Arda, and the most powerful ones, were called Valar, and the Ainur of lesser might that followed were called Maiar.

Years of the Lamps

The Years of the Lamps began shortly after the creation of Arda by the Valar. After the Valar entered the world, there was a light veiling the ground. The Valar took this light and concentrated it into two large lamps, Illuin and Ormal. The Vala Aulë forged great towers, one in the furthest north, and another in the deepest south. The Valar lived in the middle, at the island of Almaren. The end of the Years of the Lamps was marked by Melkor's destruction of the Two Lamps.

Years of the Trees

Shortly after the destruction of the Two Lamps, Yavanna made the Two Trees, named Telperion (the silver tree) and Laurelin (the gold tree) in the land of Aman, where the Valar now lived. The Trees illumined Aman, leaving Middle-earth in darkness.

The Valar had captured Melkor and placed him in chains in Aman. After he appeared to repent and was released, he sowed great discord among the Elves, and stirred up rivalry between the Ñoldorin King Finwë's two sons Fëanor and Fingolfin. Out of jealousy and hatred for the Silmarils—three gems crafted by Feänor that contained the light of the Two Trees—he stole them, killing Finwë who was guarding the jewels; then with the help of the creature Ungoliant he destroyed the Two Trees and escaped to Middle-earth.

Bitter at the Valar's inactivity, Feänor and his house left to pursue Melkor, cursing him with the name 'Morgoth'. A larger host, commanded by Fingolfin followed him. They reached the Telerin port-city of Alqualondë, and were forbidden to use the Telerin ships. Feänor decided to take them by force and thus the first Kinslaying ensued and only by the strength in numbers were the Teleri overcome and their fair ships stolen.

Feänor's host sailed on the vessels, and burned them when he arrived in Middle-earth. Left behind, Fingolfin and his company crossed over to Middle-earth through the Grinding Ice in the far north. Around the same time, but separately, Galadriel and Celeborn set sail for Middle-earth without the permission of the Valar.

Years of the Sun

The Years of the Sun began when the Valar made the Sun and the Moon out of the final fruit of Laurelin and the final flower of Telperion and set them in the heavens. Thereafter years were reckoned in Middle-earth as they are in our own real world. The First Age of the Children of Iluvatar continued into this new reckoning of time.

Ages of the Children of Iluvatar

First Age

Feänor was soon lost in an attack on Morgoth's Balrogs - but his sons survived, and founded realms; the kingdoms of the House of Fingolfin.

The Long Peace lasted hundreds of years; during which time Men arrived over the Blue Mountains. But the peace was not to last; and one by one the kingdoms — even the hidden ones of Gondolin and Doriath — fell.

At the end of the age, all that remained of free Elves and Men in Beleriand was a settlement at the mouth of the River Sirion and another settlement on the isle of Balar. Eärendil had possession of a Silmaril, which his wife Elwing's ancestors Beren and Lúthien had taken from Morgoth. But the Feänorians had a claim on the Silmaril still and so there was another Kinslaying. Eärendil and Elwing took the Silmaril across the Great Sea, to beg the Valar for aid.

They responded. Melkor was exiled into the Void; and most of his works were destroyed. This came at a terrible cost, as Beleriand itself was sunk.

Second Age

The Men who had remained faithful were given the island of Númenor, in the middle of the Great Sea; whilst the Elves were allowed to return home.

The Númenoreans became great seafarers, but became jealous of the Elves for their immortality. Meanwhile, in Middle-earth it became apparent that Sauron, Morgoth's chief servant, was still active. He worked with Elven smiths in Eregion on the craft of rings, and forged the One Ring to dominate them all. The Elves noticed this and removed theirs.

Towards the end of the age, the Númenoreans were growing increasingly proud. King Ar-Pharazôn humbled even Sauron and brought him to Númenor as a hostage. Sauron worked his way into Pharazôn's court, and became high priest in a cult of Melkor. Eventually, Pharazôn was persuaded to attempt to invade Aman, promised that immortality would result.

Amandil, chief of the faithful, sailed westward to warn the Valar of this. His son Elendil and grandsons Isildur and Anárion prepared to flee eastwards. When the King's men had landed on Aman, the Valar lay down their guardianship of the world and called for Iluvatar to intervene.

The world was changed into a sphere, and the straight road from Middle-earth to Aman was broken. Númenor was utterly destroyed, as was the fair body of Sauron. Elendil and his sons founded the realms of Gondor and Arnor.

Sauron arose again and challenged them. The Elves allied with the Men to form the Last Alliance which defeated him. His One Ring was taken from him by Isildur, but not destroyed.

Third Age

The Third Age saw the rise in power of the realms of Arnor and Gondor, and their fall. Arnor was divided into three petty Kingdoms, which fell one by one, whilst Gondor fell victim to Kin-strife, plague, wainriders, and corsairs.

By the time of The Lord of the Rings, Sauron had recovered again, and was seeking the One Ring. He discovered that it was in the possession of a Hobbit named Baggins, and sent out the Ringwraiths to find him and retrieve it.

The Ring-bearer, Frodo Baggins, is sent to Rivendell, where it is decided that the One Ring must be destroyed once and for all — and it can only be unmade in the fiery depths of Mount Doom where it was forged. He sets out on this quest with eight other companions who comprise The Fellowship of the Ring.

After a long and difficult journey, he and Samwise Gamgee finally complete the mission, succeeding largely due to an unforeseen event that was out of their control. Sauron is thus destroyed forever and they are lauded as heroes.

Fourth Age and after

The end of the Third Age marked the end of the involvement of the Elves in Human affairs, despite a short-lived revival of Elven presence in Gondor under Legolas. Most Elves that have lingered in Middle-earth leave for Valinor — those that remain behind "fade", and eventually diminish. A similar fate happens to the Dwarves: although Erebor becomes an ally of the Reunited Kingdom and there are indications Khazad-dûm is refounded, and a colony is established under Gimli in the White Mountains, they become ever more reclusive, and disappear from human history. Morgoth's creatures are almost wiped out and never recover. During the later Fourth Age the tales of the earlier Ages turn into legends, until they are eventually thought of as fantasies, as the heirs of the Númenóreans forget their heritage.

Since then, Tolkien wrote that the ages have quickened, and he estimated that the 20th century was in the Sixth or Seventh age.